no exit dose (similar to protons) as dose is deposited preferentially in a Bragg peak

Because the dose decreases from a maximum to zero in the span of a few millimeters at the distal edge of a carbon ion treatment beam, the authors surgically placed Gore-Tex spacers between tumors and bowel prior to carbon ion radiation

Mean time between surgery and radiation was 14.5 days (range 10 to 39 days)

Doses ranged from 52.8 to 73.6 GyE (Gray equivalent)

4.2 GyE fractions

Mean follow-up = 7.2 months (range 2 to 20 months)

Results

Complications: 2 patients had adhesive ileus after operation and were treated conservatively

All patients completed the planned radiation treatment

Toxicity: There were no grade 3 toxicities observed. There were relatively few and mild toxicities

Local Control:

93% at 1 year, 83% at 2 years, 79% at 3 years

By Dose: 70% with 67.2 GyE, 87% with 70.4 GyE, and 87% with 73.6 GyE

Survival (3 year):

By Dose: 36% with 67.2 GyE, 61% with 70.4 GyE, and 81% with 73.6 GyE

Author's Conclusions

Gore-Tex is a safe and effective implant material to prevent intestinal damage from carbon ion radiation in the treatment of pelvic tumors

Clinical and Scientific Implications

Insertion of inert material between tumor and organs at risk can provide a buffer for dose fall off distal to target structures when using particle therapy. This principle should in theory also work with proton radiotherapy.

There appears to be a dose response when treating pelvic tumors with carbon ion radiotherapy, however, it is unclear why patients received various doses in this study

There was no increased incidence of infection experienced in this series. There was also minimal delay of two weeks starting radiation after the implant was placed